Wind shear caused by microbursts or other weather conditions in the vicinity of airports is extremely hazardous to aircraft during takeoff and landing. While wind shear can be dangerous at any altitude, it is particularly dangerous during takeoff and landing because the aircraft is close to the ground and cannot afford to lose altitude.
Microbursts are a principal cause of wind shear hazards. A microburst is a stream of rapid moving, downwardly directed air. The air within a microburst is cooling rapidly due to drop evaporation and possibly melting hail, both of which maintain a negative buoyancy of the air which propels it towards the ground. Microbursts are always associated with clouds and principally with severe convective storms, though microbursts have been observed after virga-like precipitation. Microbursts are typically elliptical in shape and initiate relatively high in the atmosphere. They can have a cross section of up to ten kilometers or more at higher altitudes, however, the rapid downward acceleration of the air typically causes the microburst to become narrower as it approaches the ground so that it may have a cross-section of less than one kilometer near the ground. When the air in a microburst strikes the ground, the air scoots out horizontally in a diverging pattern from the center (or nadir) of the microburst.
Due to the divergent horizontally moving air close to the ground, an aircraft encountering a microburst during takeoff or landing, first experiences a strong headwind, which increase lift, rapidly followed by a strong tailwind, which reduces lift by reducing the relative air speed of the aircraft. A significant loss of altitude can occur which, depending on the altitude of the aircraft, can cause a crash.
Due to the severe hazards possible when aircraft encounter microbursts during takeoff and landing, it is desirable to detect the presence of microbursts and other wind shear hazards around airports. One system in common use, known as the Low Level Wind shear Alert System (LLWAS), consists of an array of wind sensors in and near an airport with approximately 2.5 kilometers or less between adjacent sensors. LLWAS uses cup anemometers and wind direction sensors to sense changes in wind vectors. However, as will be explained in greater detail herein, wind speed and direction alone are not accurate indicators of microbursts.
Another system in common use utilizes scanning Doppler weather radar which can detect and track air masses. Although it is believed that Doppler radar systems are more accurate in detecting microbursts and other wind shear hazards than LLWAS, such systems are large and expensive to implement. Further, wind shear phenomena can appear suddenly, e.g., within the time it takes for the radar to complete a scan and process the received signals. Also, currently used LLWAS and, to a lesser extent, Doppler radars issue wind shear alerts when there is in fact no wind shear. As a result, pilots frequently choose to fly through reported wind shear hazard areas despite the warning. However, in response to the warning, pilots tend to increase air speed so as to reduce the likelihood of stalling if a wind shear is, in fact, present. Of course, increased air speed during landing itself presents additional safety hazards.
One proposed Doppler radar system employs a non-scanning, fixed radar positioned adjacent a runway and directed towards the glide path. Although, in such a fixed radar system, individual radars an signal processing units are significantly less costly than for scanning radar systems, in order for a fixed radar to be reliable, there must be a radar positioned adjacent every runway. Therefore, fixed Doppler radar systems are also costly.
Therefore, it is an object of the present invention to provide a low cost, accurate system for detecting and measuring microbursts and other wind shear hazards.
It is another object of the present invention to provide an improved system for detecting and measuring microbursts and other wind shear hazards.
It is a further object of the present invention to provide a microburst detection and measurement system utilizing small, low cost, low power sensor units which can be easily mounted on existing structures at an airport.
It is yet a further object of the present invention to provide a microburst detection and measurement system having sensors which transmit data concerning the monitored weather conditions to a central data processing unit without use of bulky and cumbersome cable links.
It is one more object of the present invention to provide a microburst detection and measurement system capable of continuous automatic operation without human intervention.